Concentrating Solar Power (CSP) - Technology

From energypedia

► Concentrating Solar Power (CSP) - Basics and Introduction


In concentrating solar power (CSP) power plant design there are four main collector technologies that are being applied. These technologies have to be picked site-specific and shall be discussed here. A good overview is provided by the International Energy Agency in its Technology Roadmap on Concentrating Solar Power.

The four main CSP technologies in short

CSP technology, being quite different from the more popular photovoltaic equpiment, concentrates sunlight to effectively create heat to raise steam. However, there are different types of technology working under title of CSP. In the following chapters, the idea of the “parabolic trough”, the “power tower”, the “Fresnel mirror system” (or simply “linear Fresnel”) and the “dish” will be presented.

Greenpeace International 2009

►Go to Top

Parabolic Trough

These receivers are mobile applications. They are moving on a 1-axis-tracking system according to the sun's movement. It is a simpler application for tracking the sun than a point focus system (power tower or dishes) that needs to track the sun along two axes. This system, however, consists of parallel rows of reflectors or mirrors. Absorber tubes made of stainless steel serve as the heat collectors. The selective coating on these absorber tubes allows to absorb high levels of solar radiation while only few energy is lost again through infra-red radiation. The absorber tubes are insulated in an evacuated glass envelope. The heat transfer fluid used is synthetic oil. The oil is transferred through the tubes to a heat exchanger which heats and then superheats water into superheated steam. The steam is then expanded in a turbine which runs a generator to produce electricity. The water is then cooled, condenses and returns to the heat exchangers.

Power Tower

The power tower really lives up to its promise. Compared to other CSP technologies, it can create the highest degree of temperature. Surrounded by mirrors reflecting light onto an elevated and centered tower, the power tower generates heat of about 1,000 C°.[1] By transferring the reflected concentrated solar radiation to a fluid, steam is being produced that expands on a turbine in order generate the intended electricity.[2]

Linear Fresnel

This technology uses flat mirrors that are concentrating on one focal point. Water flows through the pipe which runs directly through the focal point of the mirrors. The Linear Fresnel arrangement approximates the parabolic shape of trough systems. It is a simple receiver design that facilitates direct steam generation. Thus, heat transfer fluids are not needed while applying this technology.

Dish / Engine

Parabolic dishes concetrate the sun's rays at a focal point in the centre of the dish. Most dishes use a 1-axis-trackig system, predominantly from north to south. The sun's energy, concentrated in the focal point, is given to a heat transfer fluid which is heated up to 750°C. Sometimes even gas transfer systems are applied. The fluid or gas is then used to drive a micro turbine or Stirling engine which is attached to the receiver.


Parabolic Trough
Power Tower Central Receiver
Dish / Engine Parabolic Dish
Linear Fresnel Fresnel Linear Reflector
Grid-connected plants,
mid to high-process
(Highest single unit solar capacity to date: 80
Total capacity built:
over 500 MW and more than 10 GW under construction or proposed)
Grid-connected plants,
high temperature
process heat
(Highest single unit solar capacity to date: 20 MWe
under construction, Total capacity ~50MW with at least 100MW under
Stand-alone, small
off-grid power systems or
clustered to larger gridconnected
dish parks
(Highest single unit solar capacity to date: 100 kWe, Proposals for
100MW and 500 MW in Australia and US)
Grid connected plants, or
steam generation to be
used in conventional
thermal power plants.
(Highest single unit solar capacity to date is 5MW
in US, with 177 MW
installation under
• Commercially available
– over 16 billion kWh of
operational experience;
operating temperature
potential up to 500°C
(400°C commercially
• Commercially proven
annual net plant
efficiency of 14% (solar
radiation to net electric
• Commercially proven
investment and
operating costs
• Modularity
• Good land-use factor
• Lowest materials
• Hybrid concept proven
• Storage capability
• Good mid-term
prospects for
high conversion
efficiencies, operating
temperature potential
beyond 1,000°C (565°C
proven at 10 MW scale)
• Storage at high
• Hybrid operation
• Better suited for dry
cooling concepts than
troughs and Fresnel
• Better options to use
non-flat sites
• Very high conversion
efficiencies – peak solar
to net electric
conversion over 30%
• Modularity
• Most effectively
integrate thermal
storage a large plant
• Operational experience
of first demonstration
• Easily manufactured
and mass-produced
from available parts
• No water requirements
for cooling the cycle
• Readily available
• Flat mirrors can be
purchased and bent
on site, lower
manufacturing costs
• Hybrid operation
• Very high spaceefficiency
solar noon.
• The use of oil-based
heat transfer media
restricts operating
temperatures today to
400°C, resulting
in only moderate steam
• Projected annual
performance values,
investment and
operating costs need
wider scale proof in
commercial operation
• No large-scale
commercial examples
• Projected cost goals of
mass production still to
be proven
• Lower dispatchability
potential for grid
• Hybrid receivers still an
R&D goal
• Recent market entrant,
only small projects
Source: International Concentrating Solar Power Global Outlook Greenpeace International 2009

Storage Techologies

Using different approaches to store the excess solar energy into thermal energy storages (TES) it is possible to run a CSP plant around the clock, 24 hours a day and therefore in baseload. For storing thermal energy so-called Phase Change Materials (i.e. water) are applied to make use of the latent heat. In addition thermal-chemical storages can offer even higher storage capacities making use of the chemical reactions taking place due to adsorption and absorption. A commonly used TES is molten salt while other TES are currently under investigation (see SunShot Initiative).

Further Information


  1. Taggart, S. (2008), “Hot Stuff: CSP and the Power Tower”, in: Renewable Energy Focus, May/June 2008, pg. 52
  2. Taggart, S. (2008), “Hot Stuff: CSP and the Power Tower”, in: Renewable Energy Focus, May/June 2008, pg. 54